As an example of technologies concerning such a type of three-dimensional ultrasonic imaging apparatus, there is provided a stereoscopic ultrasonic inspection technology disclosed in Japanese Unexamined Patent Application Publication Nos. 2003-149213 and 2004-53360.
Since the three-dimensional ultrasonic imaging apparatus described in these patent documents includes an ultrasonic transducer in which a large number of piezoelectric vibrators are arranged in a matrix or an array, in a plane, using ultrasonic waves emitted and received by the ultrasonic transducer to and from the object to be inspected, it is possible to three-dimensionally visualize the states of a defect, peeling, an oxidized film, a foreign material such as a void, and peeling of a joined area of the object to be inspected, thus enabling inspection of the object to be inspected in a non-destructive manner.
Using a three-dimensional ultrasonic imaging apparatus utilizing the ultrasonic transducer including a large number of piezoelectric vibrators, it is possible to visualize the layer structure of the object to be inspected having a plurality of acoustic properties, and the states of defects, voids, and peeling, etc., by means of ultrasonic waves. However, since the imaging results of the three-dimensional image data obtained by processing an electric signal corresponding to the received reflected echo of the ultrasonic transducer become uneven according to the emitted and received patterns of the ultrasonic waves, it is difficult to determine the acceptability of the quality of the object to be inspected, correctly and quantitatively, it is therefore required to determine the inspection result by means of viewing, thus, resulting in fluctuations due to differences in opinion between individual examiners.
In a known three-dimensional image processing apparatus, for an ultrasonic image of the three-dimensional imaging data of the object to be inspected obtained by processing an electric signal corresponding to the received reflected echo of the ultrasonic wave emitted and received by the ultrasonic transducer:
(1) since the imaging data of a three-dimensional ultrasonic image becomes uneven according to the emitted and received patterns of the ultrasonic wave, it has been difficult to perform objective and quantitative inspection;
(2) since the defects in an object to be inspected are determined by means of viewing, time and manpower are required, thus resulting in possibility of occurrence of fluctuations in the determination conditions of inspection; and
(3) by using a single or a pair of ultrasonic transducers arranged in a matrix, by calculating in advance the propagation time according to propagation and refraction of an ultrasonic signal emitted and received by the transducers and generating a table, it has been required to achieve a high speed and high accuracy angle beam method when an angle beam method for performing defect testing of an object to be inspected with a curved surface or defect inspection of a welded portion is performed.